1. Field of the Invention
The present invention relates to a pulsar ring of a magnetic type rotary encoder detecting an angle of rotation and a rotating speed of a rotating body, in a motor vehicle, an industrial machine or the like.
2. Description of the Conventional Art
As a typical conventional art of a magnetic type rotary encoder, there have been known structures described in Japanese Unexamined Patent Publication No. 2003-35718.
FIGS. 13 to 15 are half cross sectional views showing a magnetic type rotary encoder in accordance with a conventional art described in Japanese Unexamined Patent Publication No. 2003-35718 by cutting with a plane passing through an axis.
The magnetic type rotary encoder shown in FIGS. 13 and 14 or FIG. 15 is constituted by a pulsar ring 100 attached to a rotating body (for example, an inner ring of a bearing unit) 120 to be measured with its rotation, and a magnetic sensor 110 arranged so as to be opposed to the pulsar ring 100.
The pulsar ring 100 is constituted by an annular holder 101 installed to the rotating body 120 and manufactured by a magnetic body metal, and a pulsar main body 102 integrally provided in a disc portion 101a of the holder 101. The pulsar main body 102 is molded by a magnetic rubber material obtained by mixing a ferrite powder to a rubber-like elastic material, and is structured such that N poles and S poles are alternately magnetized in a circumferential direction. Further, the magnetic sensor 110 is attached to a non-rotating housing (not shown) in a state of being opposed to the pulsar main body 102 so as to come close thereto in an axial direction.
In the conventional art shown in FIGS. 13 and 14, the holder 101 is constituted by the disc portion 101a provided with the pulsar main body 102, an outer circumferential tube portion 101b extending from an outer circumference thereof and having a large diameter than the rotating body 120, a mounting tube portion 101c having a smaller diameter than the outer circumferential tube portion 101b and being attached to an outer circumferential surface of the rotating body 120 in accordance with pressure insertion, and an intermediate portion 101d formed between the mounting tube portion 101c and the outer circumferential tube portion 101b. Further, the structure in FIG. 13 is different from FIG. 14, in a point that the outer circumferential portion of the pulsar main body 102 extends to the outer circumferential tube portion 101b side in the holder 101 so as to form the outer circumferential tube portion 102a. 
On the other hand, in the conventional art shown in FIG. 15, the holder 101 is constituted by the disc portion 101a provided with the pulsar main body 102, a back surface collar portion 101e folded back to a back surface side thereof, and the mounting tube portion 101c extending cylindrically therefrom and being attached to an outer circumferential surface of the rotating body 120 in accordance with pressure insertion.
In this kind of magnetic rotary encoder, if the pulsar ring 100 is integrally rotated with the rotating body 120, the N poles and the S poles of the pulsar main body 102 of the pulsar ring 100 alternately pass through a front surface of the magnetic sensor 110, whereby the magnetic sensor 110 outputs a pulse-shaped signal having a wave form corresponding to a change of a magnetic field. Accordingly, it is possible to measure the rotation of the rotating body 120 on the basis of a count of the pulse.
In this case, FIG. 16 is a half cross sectional view showing a process of pressure inserting the pulsar ring in accordance with the conventional art of FIG. 13 to the rotating body by cutting with a plane passing through an axis, FIG. 17 is an explanatory view showing a state of accumulating the pulsar rings in FIG. 13 in such a manner that their axes are approximately vertical, and FIG. 18 is a partly cross sectional view showing a part of FIG. 17.
In order to pressure insert and install the mounting tube portion 101c of the holder 101 in the pulsar ring 100 to the outer circumferential surface of the rotating body 120, there is employed a pressure inserting jig 130 constituted by an end wall portion 131 pressing the disc portion 101a of the holder 101 via the pulsar main body 102, and a circumferential wall portion 132 capable of being fitted to the outer circumferential tube portion 102a of the pulsar main body 102 in FIG. 13, as shown in FIG. 16. In other words, the pulsar ring 100 is fitted into the pressure inserting jig 130 arranged coaxially with the rotating body 120 so as to be held, and the pressure inserting jig 130 is pressed to the rotating body 120 side in this state, thereby pressure inserting the mounting tube portion 101c of the holder 101 in the pulsar ring 100 to the outer circumferential surface of the rotating body 120 so as to close fit (refer to the Japanese Unexamined Patent Publication No. 2003-35718).
In this case, in order to hold the pulsar ring 100 at the concentric position with the rotating body 120 by the pressure inserting jig 130, it is necessary to make a precision of an outer diameter of the outer circumferential tube portion 102a of the pulsar main body 102 high so as to eliminate a play in a diametrical direction between the pressure inserting jig 130 and the circumferential wall portion 132, however, it is hard to precisely form the outer circumferential tube portion 102a of the pulsar main body 102. Accordingly, it becomes hard to fit the pressure inserting jig 130 to the pulsar ring 100 due to a dispersion of the outer diameter of the outer circumferential tube portion 102a in the pulsar main body 102, and the outer circumferential tube portion 102a of the pulsar main body 102 tends to be damaged. On the contrary, if a gap a in the diametrical direction is generated, it is impossible to concentrically hold the pulsar ring 100 by the pressure inserting jig 130, and there is a risk that the pulsar ring 100 is diagonally attached or deformed by being pressure inserted to the rotating body 120 in an axially deviated state. Further, the pulsar ring 100 in FIGS. 14 and 15 generates the same problem.
Further, in the pulsar ring 100 in FIG. 13 or 14, a collar portion 101f bent to an outer circumferential side is formed at an end portion of the mounting tube portion 101c in the holder 101 in order to prevent the pulsar main body 102 made of the magnetic rubber material from being damaged by the holder 101 placed thereon at a time of being accumulated in a plurality of stages in the axial direction as shown in FIG. 17. However, if a displacement is generated in the diametrical direction between the pulsar rings 100 in the accumulated state in FIG. 17 at a carrying time or a handling time, an edge portion 101f′ formed at a cut end portion of an outer circumference of the collar portion 101f is rubbed with a surface of the pulsar main body 102, and there is a risk that the pulsar main body 102 is damaged.
On the other hand, in the conventional art shown in FIG. 15, a portion having a U-shaped cross section and being constituted by the disc portion 101a and the back surface collar portion 101e is formed in the holder 101 in accordance with a press work collapsing a metal pipe in the axial direction, it is hard to make precision of an outer diameter D of the portion constituted by the disc portion 101a and the back surface collar portion 101e high. Accordingly, there is a problem that guide by the pressure inserting jig 130 (refer to FIG. 16) becomes hard as described previously.
Further, a degreasing cleaning is executed as a preliminary treatment step at a time of integrally forming the pulsar main body 102 made of the magnetic rubber material on the holder 101, however, there is a problem that it is impossible to easily remove a working oil making an intrusion into a narrow gap 101g between contacted surfaces of the disc portion 101a and the back surface collar portion 101e at a time of press forming the holder 101. Further, the residual working oil mentioned above splashes in all directions at a time of being used, or the residual working oil flows out from the narrow gap 101g to spread to an adhesion surface at a time of vulcanizing and adhering the pulsar main body 102, and there is a risk that an adhesive failure is caused.